Gear reduction apparatus

ABSTRACT

A gear reduction apparatus includes a first gear set and a second gear set connected to a motor shaft, a clutch assembly located between the first gear set and the second gear set and being configured to occupy an engaged state and a disengaged state, wherein the engaged state enables torque transmission from the first rotatable shaft to the second rotatable shaft, and the disengaged state disables torque transmission from the first rotatable shaft to the second rotatable shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 15/171,878, filed on Jun. 2, 2016, which in a continuation of U.S. patent application Ser. No. 13/450,238, filed on Apr. 18, 2012, now U.S. Pat. No. 9,358,879, which claims the benefit of U.S. Provisional App. No. 61/476,650, filed on Apr. 18, 2011. The contents of these prior applications and patents are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

This application relates to hydrostatic transaxles generally and, in particular, to transaxles intended for use in driving a vehicle, such as a rear engine riding lawn mower.

SUMMARY OF THE INVENTION

An improved hydrostatic transaxle is disclosed herein, as described in more detail below. The transaxle can be mounted on a vehicle or other powered machine or apparatus.

A better understanding of the objects, advantages, features, properties and relationships of the invention will be obtained from the following detailed description and accompanying drawings which set forth illustrative embodiments that are indicative of the various ways in which the principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of a transaxle in accordance with the present invention.

FIG. 2 is an elevational view of the transaxle of FIG. 1.

FIG. 3 is an elevational view of a first configuration of a vehicle incorporating the transaxle of FIG. 1.

FIG. 4 is a cross-sectional view of the transaxle of FIG. 2 along line 4-4.

FIG. 5 is a partially exploded perspective view of the transaxle of FIG. 1.

FIG. 6 is a plan view of a pump assembly of FIG. 5.

FIG. 7 is a cross-sectional view of the pump assembly of FIG. 6 along line 7-7.

FIG. 8 is a partially exploded perspective view of the pump assembly of FIG. 6.

FIG. 9 is a partially exploded perspective view of certain internal components of the pump assembly of FIG. 6.

FIG. 10 is a partially exploded perspective view of an axle tube motor assembly of the transaxle of FIG. 5 with certain components, including the axle tube and fluid expansion bladder assembly, removed for clarity.

FIG. 11 is a perspective view of a dual-planetary gear reduction mechanism of the axle tube motor assembly of FIG. 10.

FIG. 12 is a perspective view of the dual-planetary gear reduction mechanism of FIG. 11 with the ring gear removed for clarity.

FIG. 13 is a partially exploded perspective view of the dual-planetary gear reduction mechanism of FIG. 11.

FIG. 13A is an elevational end view of a portion of the roller clutch of the dual-planetary gear reduction mechanism of FIG. 11.

FIG. 14 is a perspective view of a fluid expansion bladder of the transaxle of FIG. 4.

FIG. 15 is a perspective view of a fluid expansion bladder assembly utilizing the fluid expansion bladder of FIG. 14.

FIG. 16 is a perspective view showing the assembled positions of the pump end cap and motor port block of the transaxle of FIG. 1, with the axle tube removed for clarity.

FIG. 17 is a rotated perspective view of the pump end cap and motor port block of FIG. 16.

FIG. 18 is an elevational view of the pump end cap and motor port block of FIG. 17.

FIG. 19 is a cross-sectional view of the pump end cap and motor port block of FIG. 18 along line 19-19, with the axle tube shown in phantom lines.

FIG. 20 is an elevational view of a second embodiment of a transaxle in accordance with the present invention.

FIG. 21 is a cross-sectional view of the transaxle of FIG. 20 along line 20-20.

FIG. 22 is an elevational view of a second configuration of a vehicle incorporating a third embodiment of a transaxle in accordance with the present invention.

FIG. 23 is a cross-sectional view of the transaxle of FIG. 22 along line 23-23.

DETAILED DESCRIPTION OF THE DRAWINGS

The description that follows describes, illustrates and exemplifies one or more embodiments of the present invention in accordance with its principles. This description is not provided to limit the invention to the embodiment(s) described herein, but rather to explain and teach the principles of the invention in order to enable one of ordinary skill in the art to understand these principles and, with that understanding, be able to apply them to practice not only the embodiment(s) described herein, but also any other embodiment that may come to mind in accordance with these principles. The scope of the present invention is intended to cover all such embodiments that may fall within the scope of the appended claims, either literally or under the doctrine of equivalents. For clarity, the various embodiments of transaxles illustrated and described in accordance with the principles of the present invention are referred to herein as transaxle “embodiments,” while the various embodiments of vehicles incorporating certain of these transaxle assemblies are referred to herein as vehicle “configurations.” Also for clarity, the vehicle configuration illustrations only depict certain vehicle elements that directly interface with their associated transaxle embodiments such as, for example, transaxle mounting accommodations, prime mover drive arrangements and vehicle wheels.

It should be noted that in the description and drawings, like or substantially similar elements may be labeled with the same reference numerals. However, sometimes these elements may be labeled with differing numbers or serial numbers in cases where such labeling facilitates a more clear description. For example, the pump housings in the three transaxle embodiments disclosed herein are serially numbered as 42, 142 and 242 respectively, to ease recognition. Additionally, the drawings set forth herein are not necessarily drawn to scale, and in some instances proportions may have been exaggerated to more clearly depict certain features. As stated above, the present specification is intended to be taken as a whole and interpreted in accordance with the principles of the present invention as taught herein and understood by one of ordinary skill in the art. Furthermore, as used herein, the terms “vertical” and “horizontal” are applied with respect to the ground or to the embodiments as illustrated and may be approximate. It will be further understood that for clarity in certain cross-sectional views, e.g., FIGS. 4, 7, 21 and 23, certain elements such as input shaft 34, pump shaft 49, pump input shafts 149 and 249, motor output shaft 79, axles 17 a and 17 b, and pulley 115, by way of example, are not shown in cross-section, as doing so would not assist in the understanding of the invention.

FIGS. 1-19 illustrate a first embodiment of a variable speed hydrostatic transaxle 30 in accordance with the principles of the invention. Transaxle 30 generally includes a pump assembly 40 coupled to and hydraulically driving a motor assembly 70. As depicted, pump assembly 40 contains a variable displacement axial piston pump 50, while motor assembly 70 contains a fixed displacement axial piston motor 80. The output shaft 79 of axial piston motor 80 extends from both ends of cylinder block 80 b to drive both axles 17 a, 17 b of transaxle 30. In the illustrated embodiment, the axes of rotation of axles 17 a, 17 b and output shaft 79 are collinear.

A first configuration of an exemplary vehicle 10 incorporating transaxle 30 is illustrated in FIG. 3. Output shaft 12 of prime mover 11 extends through an opening in vehicle frame 20 to drive the input shaft 34 of transaxle 30. A pulley 13 attached to output shaft 12 and a horizontally oriented belt 14 cooperate to drive pulley 15 affixed to input shaft 34. As indicated, an auxiliary pulley 16 can also be driven by output shaft 12 to power a mowing deck (not shown) or other equipment (not shown) of vehicle 10. Prime mover 11 is generically illustrated in FIG. 3 and can be an internal combustion engine, an electric motor, or the like; and the pulley system shown to transfer power to transaxle 30 could be replaced with other known systems, such as a chain and cogs.

Input pulley 15, auxiliary pulley 16, and their respective drive belts can be selectively engaged or disengaged by various known means, such as a clutch or idler pulley (not shown), to thereby engage or disengage transaxle 30, a mowing deck, or other auxiliary equipment mounted on vehicle 10. Transaxle 30 is supported by a pair of generally U-shaped brackets 21, each attached to frame 20 by at least two bolts 23 or other suitable fasteners. As shown, vibration dampers 22 can be interposed between brackets 21 and frame 20, if desired, to improve ride characteristics of vehicle 10. Each of the axles 17 a and 17 b of transaxle 30 drives a wheel 18 of vehicle 10.

Pump assembly 40 is securely attached to motor assembly 70 by means of a plurality of screws 33 that attach tube bracket 32 to tube brackets 42 a and 44 a that are integrally formed on pump housing 42 and pump end cap 44, respectively. Pump end cap 44 acts as a hydraulic mounting member for pump assembly 40. Tube brackets 42 a and 44 a include bosses 42 b and 44 b, respectively, to receive screws 33 or other suitable fasteners, such as bolts or rivets, for example. At least one lug 42 h or similar anchoring feature is provided on housing 42 to secure pump assembly 40 to a vehicle frame, for example, to prevent rotation of transaxle 30 about the axis of axle tube 71 and to minimize the effect of torque forces transferred through input pulley 15 when transaxle 30 is driven. Axle tube 71, which also acts as a motor housing for axial piston motor 80, has a generally cylindrical or tubular shape, and preferably a generally circular cross section.

As shown in, e.g., FIGS. 5, 8 and 19, when pump assembly 40 is attached to motor assembly 70, two protrusions 44 g having o-ring seals 48 installed thereon are inserted through two openings 71 d formed in axle tube 71 to sealingly engage two openings 74 d formed in motor port block 74, which acts as a hydraulic mounting member for motor assembly 70. Two substantially parallel fluid passages 44 f formed in pump end cap 44 connect two kidney-shaped fluid ports 44 e formed in pump running surface 44 c of pump end cap 44 with two openings 44 h formed in the two protrusions 44 g. When control arm 63 is rotated from a neutral position, hydraulic fluid flows between fluid ports 44 e and two kidney-shaped fluid ports 74 c formed in motor running surface 74 a of motor port block 74 by way of the fluid passages 44 f and through openings 44 h to provide fluid communication between axial piston pump 50 and axial piston motor 80 in a hydraulic circuit. Two check valves or check plugs 75 having check balls 75 a are installed in ports 74 e formed in motor port block 74. Check plugs of the type shown are well-known in the art and will not be described in detail herein. The various hydraulic passages formed in pump end cap 44 and motor port block 74, such as fluid passages 44 f, may be referred to generically as hydraulic porting. The formation of such hydraulic porting into such a structure is generally well-known in the art and will not be discussed in detail herein.

The designs of axial piston pump 50 and axial piston motor 80 are also well-known in the art and will not be described in detail herein. Transaxles including hydrostatic transmissions employing pump and motor assemblies of this type are described generally in, e.g., commonly-owned U.S. Pat. No. 5,314,387, the terms of which are incorporated herein by reference. “Axial piston pump 50” and “axial piston motor 80” will be referred to herein as simply “pump 50” and “motor 80,” respectively.

Referring primarily to FIGS. 1-8, pump assembly 40 will now be described in further detail. The belt-driven input pulley 15 is attached to an input shaft 34 that is drivingly engaged to a first input bevel gear 37. Optionally, with minor modification, input shaft 34 can be driven by a shaft and coupling combination that is either directly or indirectly driven by prime mover 11. Various shaft coupling methods are well known and will not be described in detail herein. The first input bevel gear 37 drives a second input bevel gear 38 disposed on pump shaft 49 adjacent to a thrust washer 47. The input shaft 34 is supported by an input bearing 35 mounted in a bearing cap 46 of gear chamber 42 c and by a journal pocket 42 i formed in gear chamber 42 c. Bearing 35 and input shaft seal 36 are both inserted into cavity 46 a formed in bearing cap 46. Cap 46 includes a flange 46 b to retain seal 36 and bearing 35. Cap 46 is secured to gear chamber 42 c by a plurality of screws 45 or other suitable fasteners that engage bosses 42 d formed on gear chamber 42 c.

Bevel gear 37 and bevel gear 38 are both located in the internal volume 41 of gear chamber 42 c. The internal volume 41 of gear chamber 42 c can either be in communication with sump 31, as shown, or sealed from sump 31 so that the input bevel gears can be lubricated by a separate volume of oil or other lubricant, as desired. Isolating the bevel gears in gear chamber 42 c reduces contamination of the hydraulic fluid of sump 31 by particles worn from gears. As is known, ball bearings, journal bearings, bushings, etc. can be added to journal pockets and journal openings, if needed, to reduce wear and increase the service life of transaxle 30.

Pump shaft 49 is drivingly engaged to the pump cylinder block 50 b rotatably disposed on running surface 44 c of pump end cap 44. Pump shaft 49 is rotatably supported by journal pocket 44 d formed in pump end cap 44 at one end and by support opening 42 f formed in pump housing 42 proximate to its opposite end.

Referring primarily to FIGS. 4 and 9, the speed and rotational direction of pump 50, and therefore motor 80, is controlled by rotating control arm 63. Control arm 63 is attached to a trunnion arm 61 by means of tapered engagement features 61 b, as shown, or alternatively, by means of splines or other known mating features, and a screw 64, as shown, or other suitable fastener. Trunnion arm 61 is rotatably supported in opening 42 g formed in pump housing 42. Trunnion arm 61 includes a protrusion 61 a that slidingly engages a recess 60 a formed in swash plate 60. A plurality of pistons 50 a riding in cylinder block 50 b of pump 50 are in continuous contact with a thrust bearing 51 that is mounted in a recess formed in the moveable swash plate 60.

When an operator rotates control arm 63 in a clockwise or counterclockwise direction by means of controls (not shown) and linkages (not shown), swash plate 60 is moved in an arc due to its engagement with protrusion 61 a. As shown in FIG. 7, swash plate guide ribs 60 b are slidingly engaged with guide slots 42 j formed in pump housing 42 to ensure proper arcuate movement of swash plate 60. This arcuate movement of swash plate 60 changes the contact angle between the pistons 50 a of pump 50 and thrust bearing 51, thereby providing variable displacement hydraulic output to rotate motor 80 in a corresponding clockwise or counterclockwise direction at various speeds. A swash plate and trunnion arm as shown herein is described in greater detail in commonly-owned U.S. Pat. No. 8,534,060, the disclosure of which is incorporated herein by reference.

Referring primarily to FIGS. 1, 2, 4, 5, 10-13 and 13A, motor assembly 70 will now be described in further detail. Cylinder block 80 b of motor 80 is rotatably disposed on running surface 74 a of motor port block 74 and is drivingly engaged to motor output shaft 79, which is also referred to as a “motor shaft.” Similar to pump 50, a plurality of pistons 80 a riding in cylinder block 80 b of motor 80 are in continuous contact with a thrust bearing 81. Thrust bearing 81, however, is mounted at a fixed angle on a stationary swash plate 82 so that motor 80 is a fixed displacement motor.

One aspect of the invention is the use of two separate dual-planetary gear reduction mechanisms engaged to the motor shaft to permit differential capability. As illustrated in, e.g., FIGS. 4, 10-13 and 13A, motor shaft 79 has a longitudinal axis of rotation and is supported by opening 74 b formed in motor port block 74 and is drivingly engaged to a first dual-planetary gear reduction mechanism 90 a at its first end and to a second dual-planetary gear reduction mechanism 90 b at its second end. Each of the first and second gear mechanisms 90 a, 90 b includes a ring gear 91 and the following elements disposed within that ring gear 91: an inner planetary gear set 85; a roller clutch 88; and an outer planetary gear set 86. FIGS. 11-13 illustrate gear mechanism 90 b, which is structurally identical to gear mechanism 90 a. The structural and functional discussion of gear mechanism 90 b that follows applies equally to gear mechanism 90 a. Ring gear 91 has a generally circular cross-section similar to that of motor port block 74 to fit inside of axle tube 71.

Inner planetary gear set 85 includes a sun gear 96 a engaged to and driven by an end of motor shaft 79. Sun gear 96 a in turn drives a set of planet gears 95 a rotatably mounted on pins 94 carried by inner carrier 92. The planet gears 95 a, in cooperation with a static ring gear 91, work to rotate inner carrier 92. Roller clutch 88 is disposed between inner planetary gear set 85 and outer planetary gear set 86, and transfers the rotational energy of inner planetary gear set 85 to outer planetary gear set 86 upon engagement. Roller clutch 88 comprises three main elements: a plurality of ramps 92 a and high points 92 b formed on the inner diameter of inner carrier 92; roller assembly 87 with its plurality of rollers 98 retained in a cage 97; and a roller running surface 96 c formed on the sun gear 96 b of outer planetary gear set 86. Roller assembly 87 is rotatably disposed on roller running surface 96 c, the combination inset within the inner diameter of inner carrier 92. Shoulder 92 c is formed on inner carrier 92 to retain the combination axially. Outer planetary gear set 86 concludes with sun gear 96 b engaged to a set of planet gears 95 b rotatably disposed on pins 94 carried by outer carrier 93.

In the disengaged state, as illustrated in FIG. 13A, the rollers 98 of roller assembly 87 are situated adjacent high points 92 b within the inner diameter of inner carrier 92 and are free to rotate. Correspondingly, sun gear 96 b and the elements thereafter are free to rotate. This disengaged state pertains mainly to the non-driven or neutral condition when motor shaft 79 is not powered. When motor shaft 79 is powered and inner carrier 92 is rotated, the rollers 98 of roller assembly 87 will begin to move away from the high points 92 b and travel up the ramps 92 a provided nominal resistance to movement is present at the outer carrier 93, such as that provided by the weight of axles 17 a, 17 b and wheels 18. Owing to the play of rollers 98 within cage 97 and the tolerances established between ramps 92 a and roller running surface 96 c, rollers 98 become wedged between ramps 92 a and running surface 96 c to thereby firmly engage and drive sun gear 96 b. In this manner, roller clutch 88 achieves engagement, and sun gear 96 b drives the planet gears 95 b and outer carrier 93. The arrangement of ramps 92 a and high points 92 b on the inner diameter of inner carrier 92 permits forward and reverse engagement of the roller clutch 88, depending on the direction of rotation of motor shaft 79. The outer carriers 93 of gear mechanisms 90 a and 90 b are drivingly engaged to one of the axles 17 a and 17 b, respectively. Thus, a vehicle such as vehicle 10 is propelled. When transaxle 30 is returned to a neutral condition by an operator and inner carrier 92 is no longer under power, roller clutch 88 likewise returns to its disengaged state.

A primary function of the pair of roller clutches 88 in transaxle 30 is to serve as a differential, allowing axles 17 a and 17 b to be rotated at different speeds. Upon initiation of a turn by the operator of a vehicle such as vehicle 10, the wheel 18 on the larger, outer turning radius is required to rotate a greater number of times than the wheel 18 on the smaller, inner turning radius. With both roller clutches 88 in the engaged state, powering both left and right side wheels 18, the increased speed imparted to the wheel 18 executing the outer turning radius will cause disengagement of its associated roller clutch 88, permitting that wheel 18 to rotate at the increased rate while the wheel 18 on the inner turning radius propels the vehicle. Upon return to straight-line travel, the disengaged clutch will once again engage.

Axles 17 a and 17 b are each supported by a pair of bearings 72 having one or more fluid-flow openings 72 a that allow hydraulic fluid circulation in sump 31 and lubrication of axle seal 73 located at each end of axle tube 71.

One aspect of the invention is the use of a simplified means for retaining the various components within the axle tube. As illustrated, motor port block 74, gear mechanisms 90 a/90 b, and bearings 72 can be positioned and retained by upsetting or forming the material of axle tube 71 in crimping and dimpling operations. Bearings 72 are positioned and retained by crimps 71 a that engage grooves 72 c formed in the lobes 72 b of each bearing 72. Gear mechanisms 90 a/90 b are positioned and retained by a plurality of dimples 71 b that engage a corresponding plurality of indentations or recesses 91 a formed on ring gears 91 of gear mechanisms 90 a/90 b. The motor port block 74 is positioned and retained by a crimp 71 c that engages a groove 74 f formed on motor port block 74. The exact form, size and location of crimps, grooves, dimples, recesses, etc., can be modified as needed. For example, the circumferential crimps 71 a shown could be changed to shorter arcuate crimps that engage just a portion of each groove 72 c or could be changed to dimples similar to dimples 71 b to engage grooves 72 c.

As illustrated, transaxle 30 is a sealed unit. Referring to FIG. 4, transaxle 30 includes internal sump 31 formed partially by joining pump housing 42 and pump end cap 44 along a vertical seam by means of a plurality of screws 43 that engage bosses 42 e. Known sealing methods, such as an adhesive-sealant or a gasket can be used to seal this seam. Installation of various seals such as input shaft seal 36, trunnion arm seal 62, o-ring seals 48 and axle seals 73 serve to further seal transaxle 30 and help form the boundaries of sump 31. While a single sump 31 is depicted herein, in that the various areas of sump 31 are in fluid communication, this design may be considered to have a first sump formed by the pump housing 42 and a second sump formed by the axle tube 71 (i.e., the housing for the motor).

Referring to FIGS. 4, 14 and 15, an internally mounted fluid expansion bladder assembly 76 is provided to relieve case pressure from transaxle 30 and prevent leakage of hydraulic fluid from sump 31 as the fluid temperature rises and the fluid expands during operation of transaxle 30. Installation of bladder assembly 76 creates an air chamber 39 that accommodates transaxle fluid expansion and is vented to atmosphere by means of at least one opening 71 e formed in axle tube 71. Opening 71 e as illustrated in FIG. 4 is merely representational; at least one opening 71 e is positioned at or near the bottom of axle tube 71. Openings 71 e are sized and positioned to allow moisture drainage, air flow in and out of air chamber 39, and can serve as sump fluid leak indicators if visually inspected.

Bladder 77 includes an integrally-formed annular seal 77 a at each end of a flexible, tubular membrane 77 b having the shape of a hyperboloid. This configuration of bladder 77 allows the hydraulic fluid of sump 31 to pass through the axial opening formed by the tubular membrane 77 b along the line 77 c in FIGS. 14 and 15. The form of the tubular membrane 77 b helps prevent contact between tubular membrane 77 b and axle 17 b. Each end of a stiff cylindrical sleeve 78 having openings 78 a to reduce weight and allow air flow in and out of opening(s) 71 e is inserted into an annular groove 77 d formed in proximity to each seal 77 a. Cylindrical sleeve 78 provides support structure for bladder 77 and proper spacing of seals 77 a. Openings 78 a can be formed in various quantities, shapes and sizes other than those illustrated, provided cylindrical sleeve 78 has sufficient stiffness to properly support bladder 77 and facilitate ease of installation of bladder assembly 76 into axle tube 71.

Bladder assembly 76 could just as readily be installed in association with axle 17 a. Furthermore, if needed for additional case pressure relief, an additional bladder assembly 76 and opening(s) 71 e can be added in association with axle 17 a, as shown in FIG. 21 in connection with a second embodiment of a transaxle assembly 130. Various other known fluid expansion components, such as a sump vent fitting (not shown) or an external fluid expansion tank (not shown) can be employed in lieu of or in addition to bladder assembly (or assemblies) 76 to relieve case pressure during operation of transaxle 30.

In transaxle 30, the rotational axes of all shafts except the input shaft 34, i.e., the rotational axes of trunnion arm 61, pump shaft 49, motor shaft 79, and axles 17 a and 17 b, are located on a single plane represented by section line 4-4. The rotational axes of input shaft 34 and pump shaft 49 are both located on another plane, represented by section line 7-7, that is oriented perpendicular to the plane represented by section line 4-4.

Various known hydraulic circuit bypass mechanisms can be applied to transaxle 30 to facilitate manually moving vehicle 10 without opposing hydraulic resistance. This, however, may not be required as it is possible to manually move vehicle 10 when the roller clutches 88 are disengaged. Alternatively, a bypass mechanism may still be desirable in order to move vehicle 10 without inadvertently engaging roller clutches 88 (via jerky or sudden movements when pushing vehicle 10). Additionally, a parking brake, such as a wheel-engagement or tire-engagement brake mechanism may be useful to prevent vehicle 10 from rolling when transaxle 30 is in neutral or very near neutral.

As illustrated in FIGS. 20 and 21, a second embodiment of a transaxle 130 includes a pump assembly 140 having a horizontally oriented pump input shaft 149 with an attached pulley 115 that is driven by a belt (not shown) that can be oriented vertically or at various other unobstructed angles. The pump housing 142 supports an input bearing 135 that is retained by a retaining ring 152. A shaft seal 136 seals sump 131 and pump input shaft 149. Not present in this embodiment are the input shaft 34, input bevel gears 37 and 38, gear chamber 42 c, and other components associated with gear chamber 42 c of pump assembly 40.

The rotational axes of all shafts of transaxle 130, including those of trunnion arm 61, pump input shaft 149, motor shaft 79, and axles 17 a and 17 b, are located on a single plane represented by section line 21-21.

As shown in FIGS. 22 and 23, a third embodiment of an electric transaxle 230 includes a pump assembly 240 having a horizontally oriented pump input shaft 249 that is directly driven by an output shaft 255 of an electric motor 211 via coupling 256 that is depicted generically with phantom lines. Also depicted with phantom lines is a guard 257 provided to shield output shaft 255, input shaft 249, and coupling 256 from excessive contamination and contact with foreign objects or debris.

An electric motor similar to electric motor 211 is described in greater detail in commonly-owned U.S. Pat. No. 8,227,948, the disclosure of which is incorporated herein by reference. The lower housing 211 a and output shaft 255 of this embodiment have been modified and shortened in comparison to similar components of the electric motor shown and described in U.S. Pat. No. 8,227,948, so that electric motor 211 has a lower profile to allow transaxle 230 to be applied to smaller vehicles, if desired, and to reduce material requirements. The external end of output shaft 255 is configured to interface with coupling 256, as is the pump input shaft 249. As stated previously herein, various shaft coupling methods are well known and will not be described in detail herein.

Pump assembly 240 includes a pump housing 242 and a pump end cap 244 that are similar to pump housing 142 and pump end cap 44, respectively, but have been modified/extended to provide clearance for mounting the electric motor 211. Electric motor 211 is securely attached to motor assembly 270 in a manner similar to that in which pump assemblies 40, 140 and 240 are attached to motor assemblies 70, 170 and 270, respectively. A tube bracket 266 is attached to the lower housing 211 a of the electric motor 211 by means of a plurality of screws 267. Tube bracket 266 is also attached to tube bracket 268 by means of a plurality of screws 269 to secure electric motor 211 to motor assembly 270. Anti-rotation features (not shown) can be employed to prevent slippage of tube brackets 266 and 268 on axle tube 271 and to ensure proper axial alignment of the electric motor shaft 255 with the pump input shaft 249.

The rotational axes of all shafts of transaxle 230, including those of trunnion arm 261, pump input shaft 249, motor shaft 279, axles 217 a and 217 b, and the electric motor output shaft 255, are located on a single plane represented by section line 23-23, giving transaxle 230 a low height profile.

A second configuration of an exemplary generic vehicle 210 incorporating a transaxle 230 is illustrated in FIG. 22. In a manner similar to that of vehicle 10, transaxle 230 is supported by a pair of generally U-shaped brackets 221, each attached to a vehicle frame 220 by at least two bolts 223 or other suitable fasteners. As shown, vibration dampers 222 can be interposed between brackets 221 and frame 220, if desired, to improve ride characteristics of vehicle 210. Each of the axles 217 a, 217 b of transaxle 230 drives a wheel 218 of vehicle 210.

Vehicle 210 includes a battery or battery set 225 to provide power to the electric motor 211 of transaxle 230 and a controller 226 to regulate the speed, etc., of electric motor 211. In this embodiment of transaxle 230, the electric motor 211 can be run at a relatively constant high speed to ensure adequate torque to move vehicle 210, the speed and forward/reverse direction of which is hydraulically controlled by rotating control arm 263. Because electric motor 211 can be run at a relatively constant speed with output shaft rotation in just one direction, control of electric motor 211 is simplified, enabling use of a simple, low cost controller 226.

While one or more specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any equivalent thereof. 

What is claimed is:
 1. A drive assembly, comprising: a motor driving a motor shaft having a first end and a second end; a first gear reduction mechanism driven by the first end of the motor shaft and driving a first axle, and a second gear reduction mechanism driven by the second end of the motor shaft and driving a second axle; wherein the first gear reduction mechanism and the second gear reduction mechanism each separately comprise: an inner planetary carrier disposed in a ring gear; an inner planetary gear set comprising a plurality of inner planetary gears mounted on the inner planetary carrier, wherein the plurality of inner planetary gears are engaged to the ring gear and rotate about an inner sun gear, and the inner sun gear is driven by the respective first end or second end of the motor shaft; an outer planetary carrier disposed in the ring gear; an outer planetary gear set comprising a plurality of outer planetary gears mounted on the outer planetary carrier, wherein the plurality of outer planetary gears are engaged to the ring gear and rotate about an outer sun gear, and the outer sun gear drives the respective first axle or second axle; and a clutch assembly disposed between the inner planetary gear set and the outer planetary gear set, the clutch assembly having an engaged state where torque is transmitted from the motor shaft to the respective first axle or second axle, and a disengaged state that enables the respective first axle or second axle to rotate independently of the motor shaft, wherein rotation of the motor shaft biases the clutch assembly to the engaged state.
 2. The drive assembly of claim 1, wherein each clutch assembly is configured such that the clutch assembly enters the disengaged state when a rotational speed of the respective first axle or second axle exceeds the rotational speed of the motor shaft.
 3. The drive assembly of claim 2, wherein each clutch assembly of the first gear reduction mechanism and the second gear reduction mechanism is a roller clutch and each roller clutch comprises: a plurality of ramps and high points disposed on an inner diameter of the inner planetary carrier; a roller assembly comprising a plurality of rollers disposed in a roller cage; and a roller running surface on which the roller assembly is mounted.
 4. The drive assembly of claim 3, wherein the roller running surface of the first gear reduction mechanism and the roller running surface of the second gear reduction mechanism are each formed on the respective outer sun gear.
 5. The drive assembly of claim 4, wherein the first gear reduction mechanism is directly engaged to the first end of the motor shaft and the second gear reduction mechanism is directly engaged to the second end of the motor shaft, and the motor shaft, first axle and second axle have collinear axes of rotation.
 6. The drive assembly of claim 5, wherein the motor is a hydraulic motor rotatably disposed on a motor port block, wherein the motor port block, the first gear reduction mechanism and the second gear reduction mechanism are disposed in a common housing, and the motor port block is located between the first and second gear reduction mechanisms.
 7. The drive assembly of claim 6, wherein the common housing has a generally circular cross-section, and the motor port block and the respective ring gears are each shaped to fit within the generally circular cross-section of the housing.
 8. The drive assembly of claim 2, further comprising: a motor port block on which the motor is rotatably disposed, wherein the motor port block, the first gear reduction mechanism and the second gear reduction mechanism are disposed in a first housing, and the motor port block is located directly between the first and second gear reduction mechanisms, and a hydraulic pump disposed in a second housing, wherein a portion of the second housing is connected to an external surface of the first housing to permit a hydraulic connection between the hydraulic pump and the motor.
 9. A drive apparatus comprising: a first gear set connected to and driven by a first rotatable shaft; a second gear set connected to and driving a second rotatable shaft; and a clutch assembly located between the first gear set and the second gear set, the clutch assembly having an engaged state where the clutch assembly transmits torque from the first rotatable shaft to the second rotatable shaft, and a disengaged state that enables the second rotatable shaft to rotate independently of the first rotatable shaft, wherein the clutch assembly enters the engaged state when a rotational force is applied to the first gear set by the first rotatable shaft, and the clutch assembly enters the disengaged state when a rotational speed of the second rotatable shaft exceeds a rotational speed of the first rotatable shaft; wherein rotation of the first rotatable shaft biases the clutch assembly to the engaged state and wherein the clutch assembly is configured such that the clutch assembly enters the disengaged state when a second rotational speed of at least a portion of the second gear set exceeds a first rotational speed of at least a portion of the first gear set.
 10. The drive apparatus of claim 9, wherein the first gear set comprises a first sun gear and a plurality of first planet gears configured to orbit the first sun gear, and the second gear set comprises a second sun gear and a plurality of second planet gears configured to orbit the second sun gear, wherein the second rotational speed is a speed of rotation of the second sun gear, and the first rotational speed is a speed of rotation of the first sun gear.
 11. The drive apparatus of claim 10, wherein the plurality of first planet gears are connected to an inner carrier, which rotates at the orbital speed of rotation of the plurality of first planet gears.
 12. The drive apparatus of claim 10, further comprising a ring gear surrounding the first gear set and the second gear set, wherein at least one of the plurality of first planet gears is in direct contact with the ring gear and at least one of the plurality of second planet gears is in direct contact with the ring gear.
 13. The drive apparatus of claim 9, wherein: the clutch assembly comprises an inner carrier and a roller running surface; the first gear set comprises a first sun gear connected to the inner carrier and a plurality of first planet gears connected to the inner carrier and engaged to the first sun gear; the second gear set comprises a second sun gear connected to the roller running surface and a plurality of second planet gears engaged to the second sun gear; and the clutch assembly enters the disengaged state when a speed of rotation of the roller running surface exceeds a speed of rotation of the inner carrier.
 14. The drive apparatus of claim 13, wherein the clutch assembly further comprises a roller assembly having a cage and a plurality of rollers, the cage at least partially retains the plurality of rollers, and the cage is configured to enable radial movement of the plurality of rollers with respect to the cage.
 15. The drive apparatus of claim 14, wherein the roller running surface contacts the plurality of rollers, and the roller running surface is static with respect to the at least a portion of the second gear set such the roller running surface rotates with the at least a portion of the second gear set.
 16. The drive apparatus of claim 9, wherein the clutch assembly comprises: a first carrier secured to and driven by the first gear set, and an inner surface of the first carrier defines a plurality of ramps and a plurality of high points; and a roller assembly having a plurality of rollers contacting the inner surface of the first carrier.
 17. A drive apparatus comprising: a motor assembly comprising a motor drivingly engaged to a motor shaft; a first gear reduction apparatus comprising: a first gear set connected to and driven by the motor shaft; a second gear set connected to and driving a first output axle; and a first clutch assembly located between the first gear set and the second gear set and having a first engaged state where the first clutch assembly transmits torque from the motor shaft to the first output axle and a first disengaged state that enables the first output axle to rotate independently of the motor shaft, and wherein rotation of the motor shaft biases the first clutch assembly to the first engaged state; and a second gear reduction apparatus comprising: a third gear set connected to and driven by the motor shaft; a fourth gear set connected to and driving a second output axle; and a second clutch assembly located between the third gear set and the fourth gear set and having a second engaged state where the second clutch assembly transmits torque from the motor shaft to the second output axle and a second disengaged state that enables the second output axle to rotate independently of the motor shaft, and wherein rotation of the motor shaft biases the second clutch assembly to the second engaged state.
 18. The drive apparatus of claim 17, wherein the motor shaft has a first axis of rotation, the first output axle has a second axis of rotation, the second output axle has a third axis of rotation, and the first, second and third axes of rotation are collinear.
 19. The drive apparatus of claim 17, further comprising: a first ring gear in which the first gear set, the second gear set, and the first clutch assembly are disposed; and a second ring gear in which the third gear set, the fourth gear set, and the second clutch assembly are disposed.
 20. The drive apparatus of claim 19, wherein the first ring gear has a first central axis, and the second ring gear has a second central axis that is collinear with the first central axis. 